Method of preparing curable coating composition from alcohol, colloidal silica, silylacrylate and multiacrylate monomer

ABSTRACT

UV curable coating compositions are provided based on the use of photoinitiator with the hydrolysis product of silylacrylate and aqueous colloidal silica. The UV curable silicone coating compositions also can contain polyfunctional acrylate. The UV curable hardcoat composition can be applied onto various substrates, for example, a polycarbonate substrate, and thereafter cured under UV radiation to produce adherent and abrasion resistant coated articles.

This application is a division of application Ser. No. 269,122, filed6/1/81, now U.S. Pat. No. 4,455,205.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to the copending applications of Rack H. Chung, Ser.No. 217,719, filed Dec. 16, 1980, now abandoned, for Abrasion ResistantUltraviolet Light Curable Hardcoating Compositions, Ser. No. 129,297,filed Mar. 11, 1980, Ser. No. 167,622, filed July 11, 1980, now U.S.Pat. No. 4,348,462 and Ser. No. 204,146, filed Nov. 5, 1980, nowabandoned.

BACKGROUND OF THE INVENTION

Prior to the present invention, thermoplastic substrates, for example,polycarbonate articles, were treated with a photocurable acrylic coatingcomposition, as shown in Moore et al., U.S. Pat. No. 4,198,465, assignedto the same assignee as the present invention. Although the use of curedpolyacrylate coatings provided durable mar resistant and chemicalresistant coatings, the ability of the cured polyacrylic coating oftendid not satisfy the abrasion resistant standards required in manyapplications.

As shown by Clark, U.S. Pat. No. 4,027,073, an acidic dispersion ofcolloidal silica in a hydroxylated silsesquioxane provides heat curablemixtures which result in valuable transparent abrasion resistantcoatings on a variety of thermoplastic substrates. It was found,however, that the cure of the hydroxylated silsesquioxane binder resinoften requires several hours, or even days to achieve acceptable marresistant properties. Efforts to accelerate the cure speed of theaforementioned silsesquioxane colloidal silica coating compositions orimpart improved abrasion resistance to the previously describedpolyacrylate coatings, have been unsuccessful.

The present invention is based on the discovery that a UV curablesubstantially solvent-free coating composition, based on the use of a UVphotoinitiator, for example, α,α-diethoxyacetophenone, can be used incombination with a silyl acrylate of the formula, ##STR1## and aqueouscolloidal silica, and optionally with acrylic monomer of the formula,##STR2## to provide a UV curable organopolysiloxane hardcoat compositioncurable to an adherent abrasion resistant coating in several seconds orless, where R is a C.sub.(1-13) monovalent radical, R¹ is a C.sub.(1-8)alkyl radical, R² is selected from hydrogen and R radicals and mixturesthereof, R³ is a divalent C.sub.(1-8) alkylene radical and R⁴ is apolyvalent organic radical, a is a whole number equal to 0 to 2inclusive, b is an integer equal to 1-3 inclusive, and the sum of a+b isequal 1 to 3 inclusive, n is an integer having a value of 2 to 4inclusive.

STATEMENT OF THE INVENTION

There is provided by the present invention, substantially solvent-freeUV curable organopolysiloxane hardcoat compositions comprising by weight

(A) 1% to 60% of colloidal silica,

(B) 1% to 50% of material resulting from the hydrolysis of silylacrylate of formula (1),

(C) 25% to 90% of acrylate monomer of formula (2) and

(D) 0.1% to 5% of a UV photoinitiator, where the sum of (A), (B), (C)and (D) is 100%.

R of formula (1) is more particularly selected from C.sub.(1-8) alkyl,such as methyl, ethyl, propyl, butyl, etc.; aryl radicals andhalogenated aryl radicals, for example, phenyl, tolyl, xylyl, naphthyl,chlorophenyl, etc.; radicals included within R¹ are, for example, all ofthe C.sub.(1-8) alkyl radicals included within R; radicals includedwithin R² are hydrogen and the same or different radicals includedwithin R. Divalent alkylene radicals included within R³ are, forexample, methylene, ethylene, trimethylene, tetramethylene, etc.Divalent organic radicals included within R⁴ are R³ radicals, branchedC.sub.(2-8) alkylene radicals, branched halogenated C.sub.(2-8) alkyleneradicals, branched hydroxylated C.sub.(2-8) alkylene radicals, branchedacrylate radicals, C.sub.(6-13) arylene radicals, for example,phenylene, tolylene, naphthylene, etc., halogenated C.sub.(6-13) aryleneradicals, etc.

Polyfunctional acrylate monomers included within formula (2) are, forexample, diacrylates of the formulas, ##STR3##

Included within the silyl acrylates of formula (1) are compounds havingthe formulas,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ --Si(OCH₃)₃,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ CH₂ --Si(OCH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ CH₂ --Si(OCH₃)₃,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ CH₂ CH₂ --Si(OCH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ CH₂ CH₂ --Si(OCH₃)₃,

CH₂ ═CCH₃ CO₂ --CH₂ CH₂ CH₂ CH₂ --Si(OCH₂ CH₃)₃,

CH₂ ═CHCO₂ --CH₂ CH₂ CH₂ CH₂ --Si(OCH₂ CH₃)₃,

etc.

Another of the necessary ingredients of the hardcoat composition of thepresent invention is colloidal silica. Colloidal silica is a dispersionof submicron-sized silica (SiO₂) particles in an aqueous or othersolvent medium. It is this polysiloxane backbone which provides thehardcoat composition with many of the advantages inherent in siliconeproducts such as a wide-ranging resistance to environmental extremes.

Dispersions of colloidal silica are available from chemicalmanufacturers such as DuPont and Nalco Chemical Company. Colloidalsilica is available in either acidic or basic form. However, forpurposes of the present invention it is preferable that the acidic formbe utilized. It has been found that superior hardcoat properties can beachieved with acidic colloidal silica (i.e. dispersions with low sodiumcontent). Alkaline colloidal silica also may be converted to acidiccolloidal silica with additions of acids such as HCl or H₂ SO₄ alongwith high agitation.

An example of a satisfactory colloidal silica for use in these coatingcompositions is Nalcoag 1034A, available from Nalco Chemical Company,Chicago, Ill. Nalcoag 1034A is a high purity, acidic pH aqueouscolloidal silica dispersion having a low Na₂ O content, a pH ofapproximately 3.1 and an SiO₂ content of approximately 34 percent byweight. In the examples given below the weight in grams or parts byweight of the colloidal silica includes its aqueous medium. Thus, forexample, 520 grams of Nalcoag 1034A colloidal silica represents,approximately, 177 grams of SiO₂ by weight. It should be noted, however,that the aqueous medium is utilized as a convenient way of handling thecolloidal silica and does not form a necessary part of the hardcoatcompositions of the present invention. In fact, it is to be emphasizedthat these coating compositions find particularly beneficial utility inthe fact that they may be part of a solventless system.

The term colloidal silica is intended to represent a wide variety offinely divided SiO₂ forms which can be utilized to form the hardcoatcompositions of the present invention without the necessity of undueexperimentation. Further description can be found in U.S. Pat. No.4,027,073.

Although the coating compositions may contain only one of saidpolyfunctional acrylate monomers, preferred coating compositions containa mixture of two polyfunctional monomers, preferably a diacrylate and atriacrylate. In addition, minor amounts of mono-acrylate can be used inparticular instances. Further, the UV curable compositions of thepresent invention can contain nonacrylic UV curable aliphaticallyunsaturated organic monomers in amounts up to 50% by weight of the UVcurable hardcoat compositions which include, for example, such materialsas N-vinyl pyrrolidone, styrene, etc.

When the coating compositions contain a mixture of acrylate monomers, itis preferred that the ratio, by weight, of the diacrylate to thetriacrylate be from about 10/90 to about 90/10. Exemplary mixtures ofdiacrylate and triacrylates include mixtures of hexanediol diacrylatewith pentaerythritol triacrylate, hexanediol diacrylate withtrimethylolpropane triacrylate, diethyleneglycol diacrylate withpentaerythritol triacrylate, and diethyleneglycol diacrylate withtrimethylolpropane triacrylate.

While the corresponding coatings may likewise contain the ultravioletlight reaction product of a single polyfunctional acrylate monomer,coatings containing the photoreaction product of two polyfunctionalacrylate monomers, preferably a diacrylate and triacrylate, arepreferred.

The photocurable coating compositions also contain a photosensitizingamount of photoinitiator, i.e., an amount effective to effect thephotocure in a non-oxidizing atmosphere, for example, nitrogen, of thecoating composition. Generally, this amount is from about 0.01% to about10% by weight, and preferably from about 0.1% to about 5% by weight ofthe photocurable coating composition.

As shown in the copending application of Rack Chung, Ser. No. 217,719,filed Dec. 16, 1980, now abandoned certain blends of ketone-type andhindered amine type materials are photoinitiators which are effectivefor crosslinking the above described coating compositions in air to formsuitable hard coatings upon exposure to UV radiation. As taught byChung, it is preferred that the ratio, by weight, of the ketone compoundto the hindered amine compound be from, approximately, 80/20 to 20/80.Ordinarily, 50/50 or 60/40 mixtures are quite satisfactory.

Other ketone-type photoinitiators which preferably are used in anonoxidizing atmosphere, such as nitrogen, are those selected from thegroup consisting of:

benzophenone, and other acetophenones,

benzil, benzaldehyde and 0-chlorobenzaldehyde,

xanthone,

thioxanthone,

2-clorothioxanthone,

9,10-phenanthrenenquinone,

9,10-anthraquinone,

methylbenzoin ether,

ethylbenzoin ether,

isopropyl benzoin ether,

α,α-diethoxyacetophenone,

α,α-dimethoxyacetophenone,

1-phenyl-1,2-propanediol-2-o-benzoyl oxime, and

α,α-dimethoxy-α-phenylacetopheone.

The coating compositions of the instant invention may also optionallycontain UV absorbers or stabilizers such as resorcinol monobenzoate,2-methyl resorcinol dibenzoate, etc. The stabilizers can be present inan amount, based upon the weight of the coating composition, exclusiveof any additional solvent which may optionally be present, of from about0.1 to 15 weight percent, preferable from about 3 to about 15 weightpercent. The UV cured coating composition can contain from about 1 toabout 15% by weight of stabilizers based on the weight of UV curablecoating composition.

The coating compositions of the present invention may also optionallycontain various flatting agents, surface active agents, thixotropicagents, UV light stabilizers and dyes. All of these additives and theuse thereof are well known in the art and do not require extensivediscussions. Therefore, only a limited number will be referred to, itbeing understood that any of these compounds can be used so long as theydo not deleteriously affect the photocuring of the coating compositionsand do not adversely affect the non-opaque character of the coating.

The various surface-active agents, including anionic, cationic andnonionic surface-active agents are described in Kirk-Othmer Encyclopediaof Chemical Technology, Vol. 19, Interscience Publishers, New York,1969, pp. 507-593, and Encyclopedia of Polymer Science and Technology,Vol. 13, Interscience Publishers, New York, 1970, pp. 477-486, both ofwhich are incorporated herein by reference.

In the practice of the present invention, the photocurable coatingcompositions can be made by blending together the aqueous colloidalsilica, the silyl acrylate, the polyfunctional acrylic monomer ormixtures thereof, the UV photosensitizer, and optionally any of theother aforementioned additives. In one blending procedure, the silylacrylate can be hydrolyzed in the presence of aqueous colloidal silicaand a water miscible alcohol. In another procedure the aqueous colloidalsilica can be added to the silylacrylate which has been hydrolyzed inaqueous alcohol. Suitable alcohols include, for example, any watermiscible alcohol, for example, methanol, ethanol, propanol, butanol,etc, or ether alcohols, such as ethoxyethanol, butoxyethanol,methoxypropanol, etc. In a further procedure, aqueous colloidal silicaand the silylacrylate are combined and stirred until hydrolysis has beeneffected. The hydrolysis of the silylacrylate can be accomplished atambient conditions, or can be effected by heating the hydrolysis mixtureto reflux for a few minutes.

Although the order of addition of the various ingredients in the UVcurable coating compositions of the present invention is not critical,it is preferred to add the polyfunctional acrylic monomer, or mixturethereof, to the above described mixture of hydrolyzed silyl acrylatesand colloidal silica. Preferably, the polyfunctional acrylic monomer ormixtures thereof is added to the mixture of silyl acrylate and colloidalsilica while it is stirring in a suitable hydrolysis medium, such as anaqueous solution of a water miscible alcohol as previously described.

In preparing the solventless UV curable hardcoat composition of thepresent invention, an azeotropic mixture of water and alcohol isdistilled from the formulation. In instances where no alcohol wasutilized in the initial hydrolysis mixture, sufficient alcohol can beadded to facilitate the removal of water by distillation. Othersolvents, for example, toluene, or other aromatic hydrocarbons, can beadded to facilitate the removal of water.

It has been found that at least one part of silyl acrylate per 10 partsof SiO₂ should be used in the UV curable composition to minimize theformation of gel.

The hard coat compositions of the present invention are based onsilicon-containing ingredients due to the condensation of colloidalsilica and the silyl acrylate. A variation of the silicon content of thehardcoat composition has been found to influence such physicalproperties as the abrasion resistance of the resulting hardcoat.Additional properties, for example, the adhesion lifetime of thehardcoat on a thermoplastic substrate can also be enhanced by optimizingthe formulation of the UV curable hardcoat composition. Suitablethermoplastic substrates which can be utilized in the practice of thepresent invention to produce shaped thermoplastic articles havingenhanced abrasion resistance are, for example, Lexan polycarbonate,Valox polyester, Mylar polyester, Ultem polyetherimide, PPOpolyphenyleneoxide, polymethylmethacrylate, etc., metals such as steel,aluminum, metallized thermoplastics, etc.

In order that those skilled in the art will be better able to practicethe invention, the following examples are given by way of illustrationand not by way of limitation. All parts are by weight.

EXAMPLE 1

A mixture was heated to reflux for 5 minutes consisting of 50 parts oftertiary butanol, 16.6 parts of Nalcoag 1034A, a product of the NalcoCompany of Oak Brook, Ill., and 1 part ofν-methacryloxypropyltrimethoxysilane (MAPTMS). After cooling, there wasadded 13.2 parts of a equal part mixture of hexanediol diacrylate intrimethylolpropane triacrylate. The solvent was distilled under reducedpressure. When about half of the solvent had distilled, an additional 30parts of t-butanol was added. All of the solvent was then distilled togive a clear solution. There was then added to 100 parts of the mixture1.5 parts of α,α-diethoxyacetophenone.

The above UV curable coating composition was then applied to a 4×41/4polycarbonate panel using a wire-wound bar. The treated panel was thenUV cured in a model 1202AN UV processor, manufactured by the PittsburghPlate Glass Company, at a belt speed of 20 feet per minute, under anitrogen flow of 20 scfm, at 100 psi. Adhesion testing of the resultingcured film was done by scribing the coated area with aGitterschnittprufgerat cross-hatch cutter, applying Mystik 6432 tape tothe cross-hatched area and rapidly pulling the tape from thecross-hatched area. Any coating removal by the tape constituted adhesivefailure. Abrasion resistance was determined by measuring the change inhaze (Δ%H) using a Gardner model UX10 haze meter before and after 300cycles of abrasing on a model 174 Taber Abraser equipped with CS-10Fwheels and 500 gm weights. Accelerated weathering was done by placingsamples in a QUV device sold by the Q-Panel Company of Cleveland, Ohio,set to consecutive cycles of fluorescent UV light for 8 hours at 70° C.and 4 hours of high humidity at 50° C.

In addition to the above UV curable coating composition, additionalcompositions were prepared containing higher amounts of the MAPTMS andacrylate mixture. The following results were obtained as shown in TableI, which shows the results obtained from various UV curable coatingcompositions having a constant level of colloidal silica and variouslevels of acrylic monomers and MAPTMS, where the parts of MAPTMS andacrylic monomers are based on 6 parts by weight of SiO₂ and "Adhesion"and "Abrasion Resistance (Δ%H)" are as previously defined:

                  TABLE I                                                         ______________________________________                                                            Properties of                                             Coating Formulations                                                                              Coated Polycarbonate                                      pbw MAPTMS:                                                                             pbw                    Abrasion Re-                                 6 pbw SiO.sub.2                                                                         Acrylic Monomers                                                                            Adhesion sistance, Δ % H                        ______________________________________                                        1         13.2          Pass     6.0                                          2         12.6          "        7.5                                          4         11.2          "        7.3                                          6         10            "        6.9                                          8         8.4           "        6.6                                          12        5.6           "        5.9                                          No Silane/                                                                              100           "        14.4                                         SiO.sub.2                                                                     ______________________________________                                    

The above results show that abrasion resistance is substantially reducedwhen the MAPTMS and colloidal silica are eliminated from the mixture,while the adhesion is maintained, based on the acrylic monomer usage.

EXAMPLE 2

A mixture consisting of 300 parts of t-butanol, 12 parts of MAPTMS and120 parts of Nalcoag 1034A was heated to reflux for 5 minutes and thenallowed to cool to room temperature. There was added 46 parts of anequal part mixture of hexanedioldiacrylate and trimethylolpropanetriacrylate to 72 parts of the aforedescribed solution after it wascooled. The solvent was then removed as in Example 1 resulting in theproduction of a clear solution. There was then added to 100 parts of theclear solution, 1.5 parts of α,α-diethoxyacetophenone resulting in theproduction of a UV curable coating composition.

The same procedure was repeated, except varying amounts of the acrylatemixture and Nalcoag 1034A were used. The following results were obtainedutilizing the resulting compositions as a UV curable mixture onpolycarbonate slabs, where "Adhesion" and "Abrasion Resistance" are asdefined above in Example 1:

                  TABLE II                                                        ______________________________________                                                     Properties of                                                                 Coated Polycarbonate                                             Coating Formulations     Abrasion Resistance                                  pbw Acrylic                                                                              SiO.sub.2                                                                             Adhesion  Δ % H                                      ______________________________________                                        46         13      Pass      10.4                                             28         20      "         10.0                                             21         25      "         8.0                                              15         30      "         6.2                                              12         35      "         4.0                                               6         50      "         3.9                                              ______________________________________                                    

The above results show that an increase in the colloidal silica improvesthe abrasion resistance of the resulting cured coating while a widevariation in parts by weight of the acrylic resin in the curableformulation does not substantially affect the adhesion of the resultingcured film on the polycarbonate substrate.

EXAMPLE 3

A mixture was heated to reflux for 30 minutes with stirring consistingof 500 parts by weight of t-butanol, 30 parts by weight MAPTMS and 200parts by weight of Nalcoag 1034A. The mixture was allowed to cool andthen there was added 70 parts of trimethylolpropane triacrylate and 30parts of 1,3-butyleneglycol diacrylate. The solvent was distilled underreduced pressure using a rotary evaporator and a hot water bath. A clearsolution was obtained when all of the solvent had been distilled.

A UV curable composition was made by adding 1.5 part ofα,α-diethoxyacetophenone to 100 parts of the above mixture. There werethen added to the UV curable hardcoat formulation 5 parts of2-ethylhexyl3,3-diphenyl-2-cyanoacrylate. Additional hardcoatformulations were prepared following the same procedure utilizing otherUV absorbers. The respective UV curable mixtures containing the UVabsorbers were then applied to polycarbonate panels as described inExample 1 and UV cured. The resulting coated panels were then tested foradhesion and abrasion resistance. In addition, an accelerated weatheringtest was also performed on each of the cured polycarbonate panels byplacing the panels in a QUV device as described above, sold by theQ-Panel Company of Cleveland, Ohio. The polycarbonate panels weresubjected to consecutive cycles of fluorescent UV light for 8 hours at70° C. and 4 hours of high humidity at 50° C. The following results wereobtained, where "UV absorber" is the compound added to the respectiveformulations, "Adhesion" and "Δ%H" are as previously defined and "QUVAdhesion" indicates the ability of the added stabilizer to impartimproved weathering resistance to the cured coating.

                  TABLE III                                                       ______________________________________                                                  Coating Properties                                                                                 QUV                                            UV Absorber Adhesion Δ % H.sup.300                                                                     Adhesion (hrs.)                                ______________________________________                                        no uv absorber                                                                            Pass     4.3       Fail 172                                       2-ethylhexyl                                                                              "        7.5       Pass 219                                       3,3-diphenyl-2-                                                               cyanoacrylate                                                                 Resorcinol  "        7.2       Pass 219                                       Monobenzoate                                                                  2-methyl    "        6.5       Pass 190                                       resorcinol                                                                    dibenzoate*                                                                   ______________________________________                                         *Shown in the copending application RD12772 of T.Y. Ching, assigned to th     same assignee as the present invention.                                  

The above results show that UV absorbers or stabilizers cansubstantially enhance the weatherability of cured coating compositionson thermoplastic substrates.

EXAMPLE 4

As shown in Example 2 of copending application of Rack Chung Ser. No.217,719, a mixture of 520 parts of Nalcoag 1034A and 80 parts of3-methacryloxypropyl trimethoxysilane was stirred for 1 hour at ambienttemperatures. There were then added 500 parts of cellosolve and thesolvents were removed under reduced pressure at 60° C. The thick residueis then dissolved in 32 parts of diethyleneglycoldiacrylate and 32 partsof trimethylolpropane triacrylate. The resulting material was then mixedwith 8.5 parts of benzophenone, 9 parts of methyldiethanolamine, 42parts of N-vinylpyrrolidone and 2 parts of BYK-300, a surface activeagent made by Mallinkrodt. A polycarbonate Lexan panel was then treatedwith the resulting coating composition and the treated panel was thenpassed through a PPG QC1202 UV processor at a speed of 20 feet perminute. The coating composition was applied to a Lexan polycarbonatepanel. The treated panel was then passed through a PPG QC1202 UVprocessor in air at a speed of 20 feet per minute. After 1 pass in anair atmosphere a hard cured clear coating was obtained. The coated Lexanpolycarbonate panel passed the adhesion test of Example 1 and showed a%H500 of 4 and a %H1000 of 4.6.

Although the above examples are directed to only a few of the very manyvariables which can be utilized in making the UV curable compositions ofthe present invention, it should be understood that the UV curablecompositions of the present invention include a much broader variety ofsilyl acrylates of formula (1), polyfunctional acrylate of formula (2)and colloidal silica as well as UV stabilizers which are shown in thedescription preceeding the examples.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. A method for making a solventless hardcoatcomposition which comprises(1) agitating a mixture of a water misciblealcohol, colloidal silica and a silyl acrylate of the formula, ##STR4##(2) adding acrylic monomer of the formula,

    [(R.sup.2).sub.2 C═CR.sup.2 --C--O].sub.n R.sup.4,

to the resulting mixture of (1) and (3) effecting removal of volatilesunder reduced pressure from the mixture of (2) where R is a C.sub.(1-13)monovalent organic radical, R¹ is a C.sub.(1-8) alkyl radical, R² isselected from hydrogen, R and mixtures thereof, R³ is C.sub.(1-8)alkylene, a is a whole number equal to 0-2 inclusive, b is an integerequal to 1-3 inclusive, and the sum of a+b is equal to 3 and n is aninteger from 2 to 4 inclusive.
 2. A method in accordance with claim 1,where a UV photoinitiator is added to the mixture.
 3. A method inaccordance with claim 1, where the silyl acrylate isν-methacryloxypropyltrimethoxysilane.
 4. A method in accordance withclaim 1, where the acrylate monomer is a mixture ofhexanedioldiacrylate/trimethylolpropanetriacrylate.
 5. A method inaccordance with claim 2, where the photoinitiator isα,α-diethoxyacetophenone.